Time course of expression of crn1, crn2 and actA of P. infestans during colonization of tomato. Total RNA isolated from infected leaves of tomato, 0, 1, 2, 3, or 4 d after inoculation, from noninfected leaves (TO), and from P. infestans mycelium grown in synthetic medium (MY) was sequentially hybridized with probes from the crn1, crn2, and actA genes. The approximate sizes of the transcripts are ∼1700 nucleotides for crn1 and crn2, and ∼1600 nucleotides for actA.